Critical role for Rab27a in cross presentation by controlling the delivery of NADPH oxidase to phagosomes in dendritic cells

JANCIC, CAROLINA; SAVINA, ARIEL; WASMEIER, CHRISTINA; SEABRA, MIGUEL; RAPOSO, GRAÇA; AMIGORENA, SEBASTIÁN

Edimburgo

Conferencia; 9th International Conference of Dendritic Cells; 2006

Dendritic cells (DCs) phagocytose pathogens or dying cell fragments, and present proteolytic peptides derived from these antigens in association with MHC class I molecules -a process called cross presentation. Efficient cross presentation requires partial antigen degradation which prevents destruction of certain T cell epitopes. We have previously shown that DCs posses a higly regulated control of phagosome acidification and then antigen degradation. This phenomenon involves the activation of NADPH oxidase at phagosomal membrane which maintains the pH avobe 7 for severals hours. Nevertheless, the mechanism by which NADPH oxidase is recruited to phagosomes in DCs was not explored thus far. We now show that DCs derived from ashen mice, which are defective for the small GTPase Rab27a, fail to cross present antigens efficiently due to increased phagosome acidification and antigen degradation. The recruitment of gp91phox (a membrane component of NADPH oxidase) to DCs phagosomes was markedly decreased and delayed in ashen phagosomes as compared to wt. By cryoeletron microscopy analysis, phagosomal adquisition of NADPH oxidase was decreased in ashen phagosomes by around 50 %. We then conclude that Rab27a is required for the efficient recruitment of NADPH oxidase to DC-phagosomes. Therefore, restrained phagosome acidification, under the control of Rab27a and the NADPH oxidase is critical for cross presentation in DCs.